In the course of turn-up of network access services, it is often necessary to perform one or more test and measurement operations on the local loop (twisted wire pair), such as, but not limited to loop loss (attenuation), the presence of bridge-taps or load coils, and data integrity at different segments of the cable plant. Loop loss is customarily measured by placing a signal transmitter at one termination of the loop and a measurement device at the other (far) end of the loop. The signal generated by the transmitter, which may comprise a tone of known frequency and power, is received by the measurement device to determine the insertion loss across the bandwidth of interest for the service being deployed. The measured loop loss may then be compared with existing cable records or deployment guidelines for the network access equipment.
An obvious drawback to this measurement procedure is the need to employ two pieces of test equipment at the opposite ends of the loop, which may be separated by miles of communication cable. Also, some test equipment is capable of generating only a limited set of tones, which can limit testing capabilities for new services. For a particular service, the network's access equipment may assist in troubleshooting the local loop, as many different types of equipment are capable of estimating loop loss of signal power, which may be reported through a control port.